For the control of calcium metabolism in animals and humans, and the maintenance of the physiological calcium balance, 1.alpha.-hydroxylated vitamin D metabolites are well-known regulatory agents. Particularly important in this regard is 1.alpha.,25-dihydroxyvitamin D.sub.3 (1,25-(OH).sub.2 D.sub.3), the natural hormonal form for the maintenance of calcium homeostastis in vivo, but a variety of other 1.alpha.-hydroxyvitamin D derivatives (e.g. 1.alpha.-hydroxyvitamin D.sub.3, 1.alpha.-hydroxyvitamin D.sub.2, 1.alpha.,25-dihydroxyvitamin D.sub.2), and certain fluorinated analogs, also exhibit potent calcemic activity. All of these compounds are of great practical importance as therapeutic agents for the treatment of a variety of calcium balance disorders, e.g. rickets, osteomalacia, osteoporosis, renal osteodystrophy and others. As a consequence, there has been much interest in the chemical synthesis of both the natural 1.alpha.-hydroxyvitamin D compounds and their structural analogs and the literature contains many examples of useful synthetic procedures. Summaries of the known methods are presented in several reviews, e.g. DeLuca et al. Topics Current Chem. 83, 1-65 (1979); Yakhimovich, Russ. Chem. Rev. 49, 371-83 (1980); or Jones and Rasmusson, Progress Chem. Org. Nat. Products, vol. 39, 64-121 (1980). In general, the known methods of synthesis of 1.alpha.-hydroxyvitamin D compounds are of three types, namely (a) synthesis from a suitable steroid precursor, (b) synthesis from a vitamin D precursor, i.e. by direct hydroxylation at carbon 1, and (c) total synthesis of the desired vitamin D compound from simple precursors, generally involving the coupling of a unit representing ring-A of the desired vitamin to a suitable partner representing the C/D-ring portion so as to generate the complete vitamin D structure and characteristic triene chromophore. Exemplary of this last approach, and especially relevant to the present invention, is the report by Baggiolini et al. [J. Am. Chem. Soc. 104, 2945-48 (1982)], describing the synthesis of 1.alpha.,25-dinydroxyvitamin D.sub.3. In this case, the protected alcohol of structure A below (representing ring-A of the vitamin molecule) is initially prepared and is then, after conversion to the Wittig reagent B, condensed with the separately synthesized ketone C (where in this case, R represents the side-chain of 25-hydroxycholesterol) to obtain the 1.alpha.,25-(OH).sub.2 D.sub.3 -derivative. The crucial ring A-1,3-diol unit (structure A, below) is synthesized from the monoterpene d-carvone in a procedure involving twelve synthetic steps. ##STR1##